Wafer holding pin

ABSTRACT

A wafer holder assembly includes first and second main structural members from which first and second wafer-holding arms extend. The first arm is secured to the main structural members by a graphite distal retaining member. The second arm is pivotally biased to a wafer-hold position by a graphite bias member. This arrangement provides a conductive path from the wafer to the assembly for inhibiting electrical discharges from the wafer during the ion implantation process. The assembly can further include additional graphite retaining members for maintaining the structural integrity of the assembly during the extreme conditions associated with SIMOX wafer processing without the need for potentially wafer-contaminating adhesives and conventional fasteners. The wafer-contacting pins at the distal end of the arms can be formed from silicon. The silicon pins can be coated with titanium nitride to enhance electrical contact with the wafer and to provide an abrasion resistant surface. The pins can have a limited profile to minimize the amount of pin material proximate the wafer for reducing the likelihood of electrical arcing from the wafer to the pin.

BACKGROUND OF THE INVENTION

The present invention relates generally to silicon wafer processing, andmore particularly, to devices for holding silicon wafers as they aresubjected to ion bombardment and to heat treatment.

Various techniques are known for processing silicon wafers to formdevices, such as integrated circuits. One technique includes implantingoxygen ions into a silicon wafer to form buried layer devices known assilicon-on-insulator (SOI) devices. In these devices, a buriedinsulation layer is formed beneath a thin surface silicon film. Thesedevices have a number of potential advantages over conventional silicondevices (e.g., higher speed performance, higher temperature performanceand increased radiation hardness). The lesser volume of electricallyactive semiconductor material in SOI devices, as compared with bulksilicon devices, tends to reduce parasitic effects such as leakagecapacitance, resistance, and radiation sensitivity.

In one known technique, known by the acronym SIMOX, a thin layer of amonocrystalline silicon substrate is separated from the bulk of thesubstrate by implanting oxygen ions into the substrate to form a burieddielectric layer. This technique of “separation by implanted oxygen”(SIMOX), provides a heterostructure in which a buried silicon dioxidelayer serves as a highly effective insulator for surface layerelectronic devices.

In the SIMOX process, oxygen ions are implanted into silicon, afterwhich the material is annealed to form the buried silicon dioxide layeror BOX region. The annealing phase redistributes the oxygen ions suchthat the silicon/silicon dioxide boundaries become more abrupt, thusforming a sharp and well-defined BOX region, and heals damage in thesurface silicon layer caused by the ion bombardment.

During the SIMOX process, the wafers are subjected to relatively severeconditions. For example, the wafers are typically heated to temperaturesof about 500-600 degrees Celsius during the ion implantation process.Subsequent annealing temperatures are typically greater then 1000degrees Celsius. In contrast, most conventional ion implantationtechniques do not tolerate temperatures greater than 100 degreesCelsius. In addition, the implanted ion dose for SIMOX wafers is in theorder of 1×1018 ions per square centimeter, which can be two or threeorders of magnitude greater than some known techniques.

Conventional wafer holding devices are often incapable of withstandingthe relatively high temperatures associated with SIMOX processing.Furthermore, wafer-holding structures having exposed metal areill-suited for SIMOX processes because the ion beam will inducesputtering of the metal and, thus, result in wafer contamination. Inaddition, the structure may deform asymmetrically due to thermalexpansion, which can damage the wafer surface and/or edge during hightemperature annealing so as to compromise wafer integrity and render itunusable.

Another disadvantage associated with certain known wafer holders iselectrical discharge of the wafers. If a wafer holder is formed fromelectrically insulative materials, the wafer will become charged as itis exposed to the ion beam. The charge build up disrupts theimplantation process by stripping the ion beam of space chargeneutralizing electrons. The charge built-up on the wafer can also resultin a discharge to a nearby structure via an electrical arc, which canalso contaminate the wafer or otherwise damage it.

It would, therefore, be desirable to provide a wafer holder that iselectrically conductive and is able to withstand the relatively hightemperatures and energy levels associated with SIMOX wafer processingwhile also minimizing the potential for sputter contamination.

SUMMARY OF THE INVENTION

The present invention provides a wafer holder assembly that maintainsits structural integrity and prevents the build up of electrical chargeon the wafer during the ion implantation process. Although the inventionis primarily shown and described in conjunction with SIMOX waferprocessing, it is understood that the wafer holder assembly has otherapplications relating to implanting ions into a substrate and to waferprocessing in general.

In one aspect of the invention, a wafer holder assembly includes astructural member that can be mechanically coupled to a target stagewithin an implanter system. The structural member serves as a base forthe wafer holding members and, in one embodiment, can be formed by firstand second main structural rails, generally parallel and spaced at apredetermined distance. A first wafer-holding arm rotatably extends fromdistal ends of the main structural members. In one embodiment, the firstarm includes a transverse member having first and second portions, eachof which includes a distal tip for releasably engaging a respectivewafer-contacting pin. The transverse member is rotatable such that thewafer-contacting pins, which are spaced apart on the wafer edge, applysubstantially equal pressure to the wafer.

A second wafer-holding arm extends from a proximal region of theassembly for providing a third contact point on the wafer via awafer-contacting pin. The second arm pivots about an axis defined by abearing connected to at least one main structural member to facilitateloading and unloading of the wafer from the assembly. In one embodiment,a bias member biases the second arm towards a wafer-hold position.

In another aspect of the invention, the wafer holder assembly is securedtogether by a series of retaining members to eliminate the need forconventional fasteners and adhesives, which are associated with wafercontamination. In one embodiment, a distal retainer member includes afirst end engageable with the first arm and a second end matable to themain structural members with a spring member extending between the firstand second ends. The distal retainer member is held under tension by thespring member so as to secure the first arm to the main structuralmembers while allowing the transverse member to freely rotate about thefirst axis such that the first and second pins apply equal pressure tothe wafer.

An intermediate retainer member can be coupled to the main structuralmembers in an intermediate region of the assembly. In one embodiment,the intermediate retainer member can include first and second opposedU-shaped outer members with a spring member extending therebetween. Thespring member is under tension such that the outer members remainengaged with corresponding protrusions on the bottom of the mainstructural members. The intermediate retaining member maintains thespacing of the first and second main structural members and enhances theoverall mechanical strength of the assembly.

The assembly can further include a proximal retainer member disposed inthe proximal region of the assembly. The proximal retainer memberincludes upper and lower members coupled by a proximal spring member.The upper and lower members are engaged to the main structural membersby the spring member, which is under tension.

In a further aspect of the invention, the wafer holder assembly providesa conductive path from the wafer to the assembly, which can be coupledto ground. By grounding the wafer, the build up of electrical charge onthe wafer is inhibited for preventing potentially damaging electricalarcing from the wafer during the ion implantation process. In anexemplary embodiment, the main structural members, the first and secondarms, the bias member, and the retainer members are formed from graphiteand the wafer-contacting pins are formed from silicon. These materialsprovide the necessary rigidity and electrical conductivity for the waferholder assembly to achieve optimal SIMOX wafer processing conditions. Inaddition, the likelihood of wafer contamination is reduced since onlysilicon contacts the silicon wafer and only silicon meets the ion beam,thereby minimizing wafer contamination and particle generation. Further,the graphite bias members have a substantially invariant spring constantover a wide temperature range, such as from room temperature to about600° C. The assembly can, therefore, be substantially calibrated at roomtemperature.

In yet another aspect of the invention, the wafer-contacting pins have ageometry that is effective to reduce the likelihood of electricaldischarges from the wafer. In one embodiment, the pins have a proximalportion for coupling to a distal end of the wafer-holding arms and adistal portion for holding the wafer. In one embodiment, the distalportions have an arcuate wafer-receiving neck disposed between awedge-shaped upper region and a tapered surface. The geometry of the pinupper region reduces the amount of pin material proximate the wafer soas to reduce the likelihood of electrical arcing between the wafer andthe pin during the ion implantation.

In another aspect of the invention, the wafer-contacting pins are coatedwith a relative hard, conductive material, such as titanium nitride(TiN) or titanium aluminum nitride (TiAlN). The coating provides adurable, abrasion resistant surface for contacting the wafer. Inaddition, the TiN coating is more conductive than silicon, from whichthe pin is formed, to enhance electrical contact between the wafer andthe pin thereby increasing the amount of current, i.e., charge build up,flowing from the wafer. The TiN coating also prevents so-calledwafer-bonding between the wafer and the pin.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a wafer holder assembly in accordancewith the present invention;

FIG. 2 is a front view of the wafer holder assembly of FIG. 1;

FIG. 3 is a side view of a first arm that forms a part of the waferholder assembly of FIG. 1;

FIG. 4. is a top view of the first arm assembly of FIG. 3;

FIG. 5 is a perspective view of a distal region of the wafer holderassembly of FIG. 1;

FIG. 6 is a top view of the distal region of FIG. 5;

FIG. 7 is a perspective view of first and second cross members that areengageable with the first arm assembly of FIG. 3;

FIG. 8 is a side view of a distal retaining member that forms a part ofthe wafer holder assembly of FIG. 1;

FIG. 9 is a side view of an alternative embodiment of the distalretaining member of FIG. 8;

FIG. 10 is a side view of a further alternative embodiment of the distalretaining member of FIG. 8;

FIG. 11 is a partial side view of a proximal portion of the wafer holderassembly of FIG. 1;

FIG. 12 is a bottom view of a proximal portion of the wafer holderassembly of FIG. 1;

FIG. 13 is a bottom view of an intermediate retaining member that formsa part of the wafer holder assembly of FIG. 1;

FIG. 14 is a partial side view of a proximal retaining member that formsa part of the wafer holder assembly of FIG. 1;

FIG. 15 is a perspective view of a further embodiment of a wafer holderassembly in accordance with the present invention;

FIG. 16A is a perspective view of a wafer-contacting pin that forms apart of the wafer holder assembly of FIG. 1;

FIG. 16B is a side view of the wafer-contacting pin of FIG. 15;

FIG. 17 is a side view of the wafer-contacting pin of FIG. 15 shownholding a wafer;

FIG. 18 is a perspective view of a wafer-contacting pin in accordancewith the present invention;

FIG. 19 is a top view of the wafer-contacting pin of FIG. 18;

FIG. 20 is an angled view of the wafer-contacting pin of FIG. 18

FIG. 21 is a side view of the wafer-contacting pin of FIG. 18;

FIG. 22 is a front view of the wafer-contacting pin of FIG. 18; and

FIG. 23 is a cross-sectional view of the wafer-contacting pin of FIG. 20along line 23—23.

DETAILED DESCRIPTION

The present invention provides a wafer holder assembly that iswell-suited for SIMOX wafer processing, which includes the use ofrelatively high ion beam energies and temperatures. In general, thewafer holder assembly has a structure that maintains its integrity andreduces the likelihood of wafer contamination during extreme conditionsassociated with SIMOX wafer processing. The wafer holder assembly can beformed from electrically conductive materials to provide an electricalpath from the wafer to ground for preventing electrical charging of thewafer, and possible arcing, during the ion implantation process.

FIGS. 1-2 show a wafer holder assembly 100 in accordance with thepresent invention. The assembly includes first and second mainstructural rail members 102,104 that are substantially parallel to eachother and spaced apart at a predetermined distance. In the exemplaryembodiment shown, the main structural members 102,104 are generallyC-shaped. A first wafer-holding arm 106 is rotatably secured to a distalend 108 of the holder assembly and a second wafer-holding arm 110 ispivotably secured to the assembly at a generally proximal region 112 ofthe assembly. The first arm 106 includes a transverse member 114 havingfirst and second portions 116,118 each of which terminates in arespective distal end 120,122. Wafer-contacting pins 124,126 are securedto the distal ends 120,122 of the first and second arm portions. Thefirst arm 106 is rotatable about a first axis 128 that is generallyparallel to the first and second main structural members 102,104. Byallowing the first arm 106 to rotate about the first axis 128, the firstand second arm portions apply substantially equal pressure to the waferedge via the spaced apart wafer-contacting pins 124,126.

The second arm 110 is pivotable about a second axis 130 that isgenerally perpendicular to the main structural members 102,104 tofacilitate loading and unloading of the wafers. A wafer-contacting pin132 is affixed to the distal end 134 of the second arm to provide, incombination with the pins 124,126 coupled to the first arm, three spacedapart contact points to securely hold the wafer in place.

Typically, placement of the pins about the circumference of the wafer islimited by a notch or “significant flat” in the wafer that is used fororientating the wafer on the holder assembly. Some processing techniquesinclude rotating the wafer a quarter turn, for example, one or moretimes during the implantation process to ensure uniform doping levels.

The wafer holder assembly can further include a series of retainingmembers for securing the components of the assembly together without theneed for conventional fasteners and/or adhesives. It is understood thatadhesives can vaporize or outgas during the ion implantation process andcontaminate the wafer. Similarly, conventional fasteners, such asexposed metal screws, nuts, bolts, and rivets can also contaminate thewafer. In addition, such devices may have incompatible thermalcoefficients of expansion making the assembly prone to catastrophicfailure.

In one embodiment, the assembly includes a distal retaining member 136coupling the first arm 106 to the assembly and an intermediate retainingmember 138 affixed to a bottom of the assembly to maintain the spacingof the first and second main structural members 102,104 in a middleregion 140 of the assembly. The assembly can further include a proximalretaining member 142 securing the structural members in position at theproximal region 112 of the assembly.

FIGS. 3-7 (shown without the wafer-contacting pins), in combination withFIGS. 1 and 2, show further details of the wafer holder assemblystructure. The first arm 106 includes a support member 144 extendingperpendicularly from the transverse member 114 (FIGS. 3-4). The supportmember 144 includes an intermediate region 146 and an arcuate couplingmember 148. A bearing member 150 extends through a longitudinal bore 152in the intermediate region 146 of the support member 144 (FIGS. 3-4).

A first cross member 154 is matable with the distal ends 156,158 of themain structural members 102,104 and a second cross member 160 is matableto the main structural members at a predetermined distance from thefirst cross member 154 (FIGS. 5-6). The first and second cross members154,160 are adapted for mating with opposite is edges of the mainstructural members 102,104. It is understood that notches can be formedin the various components to receive mating components. Each of thefirst and second cross members 154,160 includes a respective bore162,164 for receiving an end of the bearing member 150. (FIG. 7). In oneembodiment, the bearing member is a rod having each end seated withinrespective sleeve members 166,168 disposed within an aperture in thecross members 154,160. The sleeve members 166,168 allow the first arm106 to freely rotate while minimizing particle generation due tographite on graphite contact during rotation of the first arm. In oneembodiment, the sleeves are formed from a hard, insulative material,such as aluminum oxide (sapphire).

FIG. 8, in combination with FIGS. 1 and 2, show further details of thedistal retaining member 136 having a first end 170 with a first notch172 for coupling to one of the main structural members 102 and a secondnotch 174 for engaging the coupling member 148 (FIG. 3) of the firstarm. A second end 176 of the distal retaining member 136 is matable tothe intermediate region 140 of the assembly. Indents 178 can be formedin the main structural members 102,104 to facilitate engagement of thesecond end 176 to the assembly (FIG. 1).

FIGS. 9-10 show alternative embodiments of the distal retaining memberin the form of a helical spring 136′ and a bellows 136″, respectively.It is understood that one of ordinary skill in the art can readilymodify the geometry of the retaining members.

In one embodiment, the distal retaining member 136 is under tension soas to apply a force having a direction indicated by arrow 180 (FIG. 5)on the coupling member 148 of the support member. The force applied bythe distal retaining member 136 pressures a neck 182 (FIG. 3) of thesupport member against the second cross member 160. The applied forcealso pressures the first cross member 154, via the bearing member 150,against the main structural members 102,104 as the second cross member160 functions as a fulcrum for the support member 144. However, thetransverse portion 114, as well as the support member 144 of the firstarm, freely rotate about the first axis 128, i.e., the bearing member150, such that the pins 124,126 at the distal ends of the first armportions 116,118 provide substantially equal pressure on the wafer.

FIGS. 11 and 12 (bottom view), in combination with FIGS. 1 and 2, showfurther details of the second proximal region 112 of the wafer holderassembly 100. FIG. 11 is shown without the second main structural member104 for clarity. First and second stop 110 against the stop members184,186, e.g., the wafer-hold position. The bias member 190 includes aU-shaped outer portion 192 having a first end 194 mated to the firststructural member 102 and a second end 196 coupled to the secondstructural member 104 (FIG. 12). A spring portion 198 of the second biasmember includes one end abutting the second arm member 110 and the otherend extending from a bottom of the U-shaped outer member 192.

The second arm 110 pivots at its bottom end about a second bearingmember 200 disposed on the second axis 130, which is generallyperpendicular to the main structural members 102,104. The second bearingmember 200 extends through a bore in the second arm with each end of thebearing member being seated in a sleeve inserted within a respectivemain structural member 102,104. Rotation of the second arm 110 islimited by respective brace members 202,204 extending from the mainstructural members 102,104.

FIG. 13 (bottom view), in combination with FIGS. 1 and 2, shows furtherdetails of the intermediate retaining member 138, which is mated to themain structural members 102,104 in the intermediate region 140 of theassembly. The intermediate retaining member 138 includes first andsecond opposing U-shaped outer members 206,208 with a spring member 210extending therebetween. The first outer member 206 has first and secondarms 212,214 for mating engagement with corresponding notchedprotrusions 216,218 formed on the bottom of the main structural members102,104. Similarly, the second outer member 208 includes arms that arematable with notched protrusions 220,222. In one embodiment, theU-shaped outer members 206,208 are forced apart to facilitate mating tothe protrusions. Upon proper positioning, the outer members 206,208 arereleased such that spring member 210 biases the outer members againstthe protrusions. The intermediate retaining member 138 is effective tomaintain the spacing between the first and second main structuralmembers 102,104 and enhance the overall mechanical strength of theassembly.

FIG. 14 shows the proximal retaining member 142, which providesstructural rigidity in the proximal region 112 of the wafer holderassembly. In one embodiment, the proximal retaining member 142 includesupper and lower members 224,226 coupled by a spring member 228. Thespring member 228 can be engaged to the main structural members suchthat the spring member is under tension. The proximal retaining member142 can include a protruding member 230 having a slot 232 formedtherein.

As shown in FIG. 15, the assembly 100 is matable with a rotatable hubassembly 250 to which a series of wafer holder assemblies can besecured. A shield 252 can be secured to the proximal region 112 of theassembly to protect exposed regions of the assembly from beam strike.The shield 252 prevents sputtering from the assembly components, as wellas any metal devices used to affix the assembly to the hub 250, duringthe ion implantation process. In addition, the assembly components arenot heated by direct exposure to the ion beam. In one embodiment, anedge of the shield 252 is captured in the slot 232 (FIG. 14) located inthe proximal retaining member 142.

It is understood that the shield 252 can have a variety of geometriesthat are effective to shield the assembly components from beam strike.In one embodiment, the shield 252 is substantially flat with an arcuateedge 254 proximate the second wafer-holding arm 110 to increase theshielded region of the assembly.

It is further understood that the shield can be formed from variousmaterials that are suitably rigid and are opaque to the ion beam. Oneexemplary material is silicon having properties that are similar to asilicon wafer.

The wafer-contacting pins 124,126,132 coupled to ends of thewafer-holding arms are adapted for contacting and securing the wafer inthe wafer holder assembly 100. In general, the pins should applysufficient pressure to maintain the wafers in the holder assembly duringthe load and unload process in which the wafers are manipulated througha range of motion that can include a vertical orientation. However,undue pressure on the wafers should be avoided since damage to the wafersurface and/or edge can result in the formation of a slip line duringthe subsequent high temperature annealing process. In addition, thewafer-contacting pins should not electrically insulate the wafer fromthe assembly. Further, the pins should be formed from a material thatminimizes contamination of the wafer.

FIGS. 16A-B show a wafer-contacting pin 300 adapted for use with a waferholder assembly in accordance with the present invention. The pin has adistal portion 302 having a geometry adapted for holding the edge of awafer and a proximal portion 304 having a contour complementing acorresponding channel formed in the ends of the wafer arms 106,110 (FIG.1). It is understood that a variety of shapes and surface features canbe used to securely and releasably mate the pin 300 to the wafer-holdingarms.

The distal portion 302 of the pin includes a ridge 306 extending from anarcuate wafer-receiving groove 308 in the pin. A tapered surface 310extends proximally from the groove 308. As shown in FIG. 17, the pinshould contact the top 352 and bottom 354 of the wafer 350 to preventmovement and/or vibration of the wafer as the holder assembly is rotatedduring the implantation process. In addition, the tapered surface 310provides a ramp on which the wafer edge may first contact and slide uponduring the wafer load process until meeting the ridge 306.

FIGS. 18-23 show a wafer-contacting pin 400 in accordance with thepresent invention having a more limited profile. The pin 400 includes adistal portion 402 for holding a wafer and a proximal portion 404 forcoupling to the arm ends. The distal portion 402 of the pin is roundedto minimize the amount of pin material proximate the wafer edge forreducing the likelihood of electrical discharge from the wafer to thepin. In addition, the pin geometry is optimized to maximize the distancebetween the wafer edge and the pin except at the wafer/pin contactinterface. Further, the wafer-contacting region of the pin 400 should besmooth to minimize the electric field generated by a potentialdifference between the wafer and the pin. The pin should also minimizethe wafer/pin contact area.

The distal portion 402 of the pin includes a wafer-receiving groove orneck 406 disposed between a wedge-shaped upper region 408 and a taperedsurface 410. The neck 406 can be arcuate to minimize the contact areabetween the wafer edge and the pin. The upper region 408, including theneck 406, can taper to a point or edge 412 for reducing the amount ofpin material near the wafer edge to inhibit electrical arcing betweenthe wafer and the pin.

It is understood that the term wedge-shaped should be construed broadlyto include a variety of geometries for the pin upper region. In general,the wedge-shaped upper region broadens from a point nearest a center ofa wafer held in the assembly. Exemplary geometries include triangular,arcuate, and polygonal.

In a further aspect of the invention, a wafer-contacting pin, such asone of the pins 122,300,400 shown in FIGS. 1, 15, 18, is coated with arelatively hard, electrically conductive film, such as titanium,titanium nitride (TiN) or titanium aluminum nitride (TiAlN). The coatingprovides a relatively hard, abrasion resistant material that enhancesthe ruggedness of the pin. In the case where the pin is formed fromsilicon, the TiN coating, for example, is more conductive than thesilicon pin such that the likelihood of electrical arcing is reduced incomparison with an uncoated pin. In addition, the coating inhibitsso-called wafer bonding in which two silicon surfaces tend to sticktogether during extreme processing conditions, e.g., relatively hightemperatures. It is understood that potentially contaminating particlescan be generated when a wafer bond between a wafer and awafer-contacting pin is broken.

The coating car be applied to the pin using a variety of techniquesincluding chemical vapor deposition and reactive sputtering. Forchemical vapor deposition to provide a TiN coating, an exemplaryprecursor gas is titanium chloride. For reactive sputtering a titaniumtarget can be used and nitrogen gas can be added to an argon gasenvironment.

It is understood that the TiN or TIAlN coating can be applied to coverthe entire pin, as well as only targeted portions corresponding to thepin/wafer interface. It is further understood that the TiN coating canbe applied in discrete portions or as a continuous coating.

The thickness of the coating can vary from about 0.1 micrometers toabout 10.0 micrometers, and more preferably from about 2 micrometers toabout 5 micrometers. A preferred coating thickness is about 5micrometers.

In a further aspect of the invention, the materials for the variouscomponents are selected to provide desired features of the assembly,e.g., mechanical durability; electrical conductivity; and minimalparticulation. Exemplary materials for the wafer-contacting pin includesilicon and graphite. It is understood that silicon is conductive in itsintrinsic state at elevated temperatures. Exemplary materials for themain structural members, the retainer members, and the bias memberinclude silicon carbide, graphite and vitreous or vacuum impregnatedgraphite, which can be coated with titanium carbide. The graphiteretainer and bias members can be fabricated from graphite sheets usingwire electron discharge machine (“wire EDM”), laser machining andconventional cutting techniques.

The graphite bias and retaining members maintain a steady, i.e.,invariant, spring constant over a wide range of temperatures. Thisallows the wafer holder assembly to be adjusted at room temperature foroperation at temperatures of 600° C. and higher, which can occur duringthe ion implantation process. The graphite components also provide aconductive pathway for grounding the wafer, even where insulativesleeves for the bearing members are used.

The wafer holder assembly of the present invention provides a structurethat withstands the relatively high temperatures and ion beam energiesassociated with SIMOX wafer processing. In addition, the likelihood ofwafer contamination is reduced since the ion beam strikes only siliconthereby minimizing carbon contamination and particle production.Furthermore, the likelihood of the electrical discharge from the waferis minimized due to the selection of conductive materials/coatings forthe assembly components and/or the geometry of the wafer-contactingpins.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

What is claimed is:
 1. A wafer holder assembly, comprising: at least onemain structural member; a first arm having a first end for holding awafer and a second end coupled to the at least one main structuralmember; and a pin having a wafer-contacting distal portion and aproximal portion coupled to the first end of the first arm, the distalportion connected to the proximal portion by a neck having a waferreceiving groove and having a wedge-shaped upper region situated abovethe wafer in use to limit the amount of pin material exposed to an ionbeam during a wafer implantation process.
 2. The wafer holder assemblyaccording to claim 1, wherein the neck of the distal portion furtherincludes a tapered surface for guiding a wafer to a wafer-hold positionin the wafer receiving groove.
 3. The wafer holder assembly according toclaim 2, wherein the wafer receiving groove is disposed between thetapered surface and the upper region.
 4. The wafer holder assemblyaccording to claim 3, wherein the wafer receiving groove is adapted forcontacting top and bottom regions of the wafer.
 5. The wafer holderassembly according to claim 1, wherein the pin is formed from a materialselected from the group of silicon and graphite.
 6. The wafer holderassembly according to claim 1, further including an electricallyconductive coating disposed on at least a wafer-contacting portion ofthe pin.
 7. The wafer holder assembly according to claim 1, wherein thepin is formed from silicon.
 8. The wafer holder assembly according toclaim 1, wherein the pin is formed from graphite.
 9. A wafer holdingpin, comprising: a distal portion for holding a wafer and a proximalportion for coupling to a wafer holder arm, the distal portion connectedto the proximal portion by a neck having a wafer receiving groove andhaving a wedge-shaped upper region situated above the wafer in use tolimit the amount of pin material exposed to an ion beam during a waferimplantation process.
 10. The wafer holding pin according to claim 9,wherein the neck of the distal portion further includes a taperedsurface for guiding a wafer to a wafer-hold position in the waferreceiving groove.
 11. The wafer holding pin according to claim 10,wherein the wafer-receiving groove is disposed between the taperedsurface and the upper region.
 12. The wafer holding pin according toclaim 11, wherein the wafer receiving groove is adapted for contactingtop and bottom regions of the wafer.
 13. The wafer holding pin accordingto claim 9, wherein the pin is formed from a material selected from thegroup consisting of silicon and graphite.
 14. The wafer holding pinaccording to claim 9, further including an electrically conductivecoating disposed on at least a wafer-contacting portion of the pin. 15.The wafer holding pin according to claim 9, wherein the pin is formedfrom silicon.
 16. The wafer holding pin according to claim 9, whereinthe pin is formed from graphite.
 17. An ion implantation system,comprising: a wafer holder assembly including at least one mainstructural member; a first arm having a first end for holding a waferand a second end coupled to the at least one main structural member; anda pin having distal wafer-contacting portion and a proximal portionreleasably engaged to the first end of the first arm, the distal portionconnected to the proximal portion by a neck having a wafer receivinggroove and having a wedge-shaped upper region situated above the waferin use to limit the amount of pin material exposed to an ion beam duringa wafer implantation process.
 18. The wafer holder assembly according toclaim 17, wherein the neck of the distal portion further includes atapered surface for guiding a wafer to a wafer-hold position in thewafer receiving groove.
 19. The wafer holder assembly according to claim18, wherein the wafer-receiving groove is disposed between the taperedsurface and the upper region.
 20. The wafer holder assembly according toclaim 19, wherein the wafer receiving groove is adapted for contactingtop and bottom regions of the wafer.
 21. The wafer holder assemblyaccording to claim 17, wherein the pin is formed from a materialselected from the group consisting of silicon and graphite.
 22. Thewafer holder assembly according to claim further including anelectrically conductive coating disposed on at least a wafer-contactingportion of the pin.
 23. The wafer holder assembly according to claim 17,wherein the pin is formed from silicon.
 24. The wafer holder assemblyaccording to claim 17, wherein the pin is formed from graphite.
 25. Awafer holding pin comprising a proximal portion for coupling to a waferholder assembly and a distal portion for holding a wafer at its edge,the distal portion connected to the proximal portion by a neck having awafer receiving groove, the surface of the groove being curved tocontact top and bottom regions of the wafer edge.
 26. The wafer holdingpin according to claim 25, wherein the neck of the distal portionfurther includes a tapered surface for guiding a wafer to a wafer-holdposition in the wafer receiving groove.
 27. The wafer holding pinaccording to claim 26, wherein the wafer-receiving groove is disposedbetween the tapered surface and the upper region.
 28. The wafer holdingpin according to claim 27, wherein the wafer receiving groove is adaptedfor contacting top and bottom regions of the wafer.
 29. The waferholding pin according to claim 25, wherein the distal portion furtherincludes a durable, abrasion-resistant electrically conductive coatingdisposed on at least a wafer-contacting portion of the pin.
 30. Thewafer holding pin according to claim 29, wherein the electricallyconductive coating has a thickness in a range of about 0.5 micrometersto about 10.0 micrometers.
 31. The wafer holding pin according to claim25, wherein the distal portion of the pin further includes a taperedsurface for guiding a wafer to a wafer-hold position in the waferreceiving groove.
 32. The wafer holding pin according to claim 31,wherein the wafer receiving groove is disposed between the taperedsurface and an upper region.
 33. The wafer holding pin according toclaim 25, wherein the pin is formed from a material selected from thegroup consisting of silicon and graphite.
 34. The wafer holding pinaccording to claim 25, wherein the pin is formed from silicon.
 35. Thewafer holding pin according to claim 25, wherein the pin is formed fromgraphite.
 36. The wafer holding pin according to claim 25, wherein thepin is formed from an electrically conductive material.